In order to provide solid state lighting sources it is possible to place on a substrate an array or “cluster” of radiation sources (of the LED type for example), using a combination of light radiation sources having different emission characteristics (in terms of the wavelength and/or intensity of the emitted flux, for example): this combination provides compensation for the variations of characteristics that may arise in the process of manufacturing the sources.
This procedure yields savings in respect of the process for manufacturers of light sources, and also improves the emission performance without appreciably increasing the fixed production costs, whereas, if a specific selection were made in terms of emission wavelength (color) and flux (light intensity) in the course of production, this could entail a rise of 10% to 20% in production costs.
The use of a combination of light radiation sources to provide this compensatory effect may make additional demands in terms of logistics and storage. However, it is possible to use the technique known as “binning”, in which the light radiation sources are arranged in distinct batches (called “bins”) on the basis of what are known as binning classes, defined according to the emission characteristics (e.g. direct operating voltage; emission wavelength and characteristics, or “color”; and flux or light intensity). An example of a solution for using light radiation sources belonging to different binning classes is described in EP 1 750 486 E1.
In various solutions, light radiation sources (referred to below as LED sources for the sake of simplicity) contained in a given bin may be placed on a reel. The sources can then be picked up from the reel, for example by using a “pick and place” machine, which places the sources on a substrate to form an array or cluster, thus providing the effect of combination by application of the principles of colorimetric theory so as to achieve the desired effects in terms of color, flux and/or supply voltage.
In various solutions, lighting devices (“light engines”) can be produced by using LEDs arranged in three to four bins, for example, these quantities being chosen so as to avoid excessive complexity and cost in respect of the production cycle and the logistical aspects associated with the use of binning. For the purposes of production, it is possible to load each pick and place machine with reels, each of which corresponds to a given bin.
Assuming, by way of example, that N bins are used to produce lighting devices each comprising a number of LEDs equal to M, then in order to provide a production batch of J devices with K LEDs per reel, (M×J)/(K×N) reels must be managed for each bin. In numerical terms, if 600 lighting modules or devices are to be produced, each comprising 32 LEDs, and 600 LEDs are available on each reel, with the LEDs arranged in four bins, then 8 reels will be used for each of the four bins. A set of reels of this type is called a “kit” of LEDs.
In various solutions it may be necessary to keep the various reels forming the LED kit in store, ensuring that each individual reel in the kit is identified and locatable for the purposes of production logistics, so that a given bin can be located in a given position of the cluster, using a dedicated program for controlling the pick and place machine for each bin.
In WO 2012/034827 A1 it is proposed to place light radiation sources (such as LEDs) taken from n different bins in sequence on the same reel, repeating the sequence of these LEDs so as to obtain the desired characteristics in the lighting device by the use of combination as described above.
This document (see for example FIG. 2 of WO 2012/034827 A1) therefore proposes the production of a packaging unit (e.g. a reel) in which the light radiation sources are arranged in successive sequences in which each sequence includes light radiation sources taken from different bins having respective light emission characteristics, the sequential order of appearance of the different bins from which the various light radiation sources are taken being repeated in an identical manner (e.g. A, B, C, D, . . . ) in the successive sequences throughout.
Using the terminology of the document in question, the light radiation sources (LEDs) are therefore arranged in the packaging unit (e.g. a reel) in such a way that the packaging unit includes a plurality of successive sequences including, in each case, a plurality of light radiation sources, in which each sequence has, respectively, a light source taken from each of the ranges of color characteristics (or “bins”), and the light radiation sources in the different bins within the sequence are, respectively, arranged in the same order in all the sequences.
In practice, if the various light sources are identified according to the different bins to which they belong, by letters such as A, B, C and D, the sequence of distribution of the light radiation sources in the packaging unit (a reel, for example) can be represented thus: A B C D A B C D A B C D A B C D A B C D A B C D, and so on, as shown by way of example in FIG. 2 of WO 2012/034827 A1).
For mounting, the prior document in question specifies (see FIG. 3 of WO 2012/034827 A1) that a cluster of the matrix type is formed from the sequence A, B, C, D, A, B, C, D, . . . , this cluster being arranged in rows and columns in a sequence that can be interpreted as a sequence ordered in rows with a return “to the start” at the end of each row, thus:
ABCDABCDABCD
In some cases at least, this solution is vulnerable to a loss of a single radiation source, due for example to the “skipping” of one of the light radiation sources in the pick-up sequence during the mounting on the substrate carried out by the pick and place machine, as a result of which the overall effect of the combination is degraded.
A generally similar problem may also arise in a cluster mounted in a regular way (in other words, without “skipping” any radiation source), if one of the radiation sources in the cluster is subject to a fault, regardless of whether the fault is “soft” (where the source emits at a lower level of luminosity than expected, although it does not stop emitting altogether) or “hard” (where the light radiation source stops emitting altogether).